Strain improvement of Aspergillus flavus for enhanced ascorbic acid production by physical and chemical mutagenesis
The demand for ascorbic acid in the food and pharmaceutical industry led to the search for hyper ascorbic acid producing strains by physical and chemical mutagenesis. Spores of Aspergillus flavus were subjected to Ultraviolet (UV) radiation (240 nm) and Ethidium Bromide (EB) (25, 50, 75 and 100 μg/ml) to develop hyper-producing mutants. The selected mutants were cultured in a liquid fermentation medium containing Brewery Spent Grain (0.6 % w/v) at pH range 4 - 8, temperature range 30 - 45 °C, agitation speed range 60 - 160 rpm for 96 h. Ascorbic acid produced was quantified by titration techniques and with High Performance Liquid Chromatography (HPLC). The UV and EB mutant strains of A. flavus gave increased ascorbic acid yields of 6.99 g/L and 7.28 g/L respectively when compared to the parental strain with ascorbic acid yield of 3.92 g/L. Optimum ascorbic acid yields were produced at 40 °C, pH 5.0 and 100 rpm at 96 h of fermentation. This study shows the potential of strain improvement for enhanced ascorbic acid production.
Keywords: Ascorbic acid; Ethidium bromide; Ultraviolet radiation; Aspergillus flavus; Mutagenesis